Systems, methods, and apparatuses for spectrum-sensing cognitive radios

ABSTRACT

Systems, methods, and apparatuses are provided for spectrum-sensing cognitive radios that are operative to detect and utilize available RF spectrum resources. The spectrum-sensing cognitive radios include at least one antenna and a frequency-agile radio front-end module in communication with the at least one antenna and configured to transmit and receive radio frequency signals via the at least one antenna. In addition, a spectrum-sensing module, which may include one or both of coarse-sensing and fine-sensing modules, may be in communication with the at least one antenna and be configured to generate RF spectrum usage information. A medium access control (MAC) module is operative to receive the RF spectrum usage information from the spectrum-sensing module. Based upon the received RF spectrum usage information, the MAC module is operative to direct a frequency of operation of the radio front-end module based at least in part on the received spectrum usage information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 60/729,036, filed Oct. 21, 2005, entitled “Systems, Methods, and Apparatuses for Spectrum-Sensing Cognitive Radios” and U.S. Provisional Application No. 60/729,035, filed Oct. 21, 2005, entitled “Systems, Methods, and Apparatuses for Spectrum-Sensing Modules,” which are both incorporated herein by reference in their entirety. In addition, this application is related to the following co-pending, commonly assigned U.S. applications, each of which is entirely incorporated herein by reference: “Systems, Methods, and Apparatuses for Coarse-Sensing Modules” filed Jul. 18, 2006, and accorded application Ser. No. 11/458,275 and “Systems, Methods, and Apparatuses for Fine-Sensing Modules,” filed Jul. 18, 2006, and accorded application Ser. No. 11/458,280.

FIELD OF THE INVENTION

The present invention relates generally to cognitive radios, and more particularly to spectrum-sensing cognitive radios.

BACKGROUND OF THE INVENTION

In the United States and in a number of other countries, a regulatory body like the FCC (Federal Communications Commission) oftentimes regulates and allocates the use of radio spectrum in order to fulfill the communications needs of entities such as businesses and local and state governments as well as individuals. More specifically, the FCC licenses a number of spectrum segments to entities and individuals for commercial or public use (“licensees”). These licensees may have an exclusive right to utilize their respective licensed spectrum segments for a particular geographical area for a certain amount of time. Such licensed spectrum segments are believed to be necessary in order to prevent or mitigate interference from other sources. However, if particular spectrum segments are not in use at a particular location at a particular time (“the available spectrum”), another device should be able to utilize such an available spectrum for communications. Such utilization of the available spectrum would make for a much more efficient use of the radio spectrum or portions thereof.

Previous spectrum-sensing techniques disclosed for determining the available spectrum have been met with resistance for at least two reasons: (1) they either do not work for sophisticated signal formats or (2) they require excessive hardware performances and/or computation power consumption. For example, a spectrum sensing technique has been disclosed where a non-coherent energy detector performs a computation of a Fast Fourier Transform (FFT) for a narrow-band input signal. The FFT provides the spectral components of the narrow-band input signal, which are then compared with a predetermined threshold level to detect a meaningful signal reception. However, this predetermined threshold level is highly-affected by unknown and varying noise levels. Moreover, the energy detector does not differentiate between modulated signals, noise, and interference signals. Thus, it does not work for sophisticated signal formats such as spread spectrum signal, frequency hopping, and multi-carrier modulation.

As another example, a cyclo-stationary feature detection technique has been disclosed as a spectrum-sensing technique that exploits the cyclic features of modulated signals, sinusoid carriers, periodic pulse trains, repetitive hopping patterns, cyclic prefixes, and the like. Spectrum correlation functions are calculated to detect the signal's unique features such as modulation types, symbol rates, and presence of interferers. Since the detection span and frequency resolution are trade-offs, the digital system upgrade is the only way to improve the detection resolution for the wideband input signal spectrum. However, such a digital system upgrade requires excessive hardware performances and computation power consumption. Further, flexible or scalable detection resolution is not available without any hardware changes.

Accordingly, there is a need in the industry for cognitive radios that allow the available spectrum to be utilized while minimizing hardware and power consumption requirements.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, there is a cognitive radio for utilizing available frequency spectrum resources. The cognitive radio may include spectrum sensing in conjunction with frequency-agile operation. The spectrum sensing, which may be comprised of coarse and/or fine spectrum sensing, may be performed in analog in accordance with an embodiment of the invention. The coarse-sensing technique may utilize wavelet transforms to provide a multi-resolution sensing feature known as Multi-Resolution Spectrum Sensing (MRSS), according to an embodiment of the present invention. The fine spectrum sensing technique may utilize the beneficial properties of the autocorrelation function to provide for Analog Auto-Correlation (AAC), according to an embodiment of the present invention. Spectrum sensing in accordance with an embodiment of the present invention may thus detect a variety of sophisticated signal formats adopted in the current and emerging wireless standards including IS-95, WCDMA, EDGE, GSM, Wi-Fi, Wi-MAX, Zigbee, Bluetooth, digital TV (ATSC, DVB), and the like. Moreover, the analog implementation of these spectrum sensing techniques in accordance with an embodiment of the present invention offers several features, including one or more of fast detection for a wideband frequency range, low power consumption, and low hardware complexity.

In accordance with an embodiment of the present invention, there is a cognitive radio system. The cognitive radio system includes at least one antenna, a radio front-end module in communication with the at least one antenna and configured to transmit and receive radio frequency signals via the at least one antenna, and a spectrum-sensing module in communication with the at least one antenna and configured to generate radio frequency (RF) spectrum usage information. The cognitive radio system further includes a medium access control (MAC) module operative to receive the RE spectrum usage information from the spectrum-sensing module, where the MAC module is operative to direct a frequency of operation of the radio front-end module based at least in part on the received spectrum usage information.

According to an aspect of the present invention, the at least one antenna may include a first antenna and a second antenna, where the radio front-end module may be in communication with the first antenna and the spectrum-sensing module may be in communication with the second antenna. According to another aspect of the present invention, the spectrum-sensing module may include at least one of a coarse-sensing module and a fine-sensing module, where the coarse-sensing module provides spectrum usage information associated with spectrum occupancy and the fine-sensing module provides spectrum usage information associated with signal identification. The spectrum usage information associated with signal identification may relate to at least one of modulation schemes and frame types. The spectrum sensing module may generate spectrum usage information associated with spectrum occupancy and upon a request by the MAC module, may generate spectrum usage information associated with signal identification. According to another aspect of the present invention, the cognitive radio system may further include an analog-to-digital converter that digitizes the generated spectrum usage information, where the digitized spectrum usage information may received by the medium access control module. According to yet another aspect of the present invention, the spectrum-sensing module may be an analog, wideband spectrum-sensing module.

According to another embodiment of the present invention, there is a method for implementing a cognitive radio system. The method includes receiving radio signals at a spectrum-sensing module and generating via the spectrum-sensing module, spectrum information based at least in part on the received radio signals. The method further includes receiving the spectrum information at a medium access control module, determining via the medium access control module, a non-occupied spectrum based at least in part upon the spectrum information, and reconfiguring a transceiver to operate in the non-occupied spectrum.

According to an aspect of the present invention, generating spectrum information may include generating information for determining spectrum occupancy. According to another aspect of the present invention, generating spectrum information may include generating information for signal identification upon a request from the medium access control module. In addition, the spectrum sensing module may include a module that generates the information for determining spectrum occupancy. The spectrum sensing module may also include a module that generates the information for signal identification. According to yet another aspect of the present invention, receiving radio signals at a spectrum-sensing module comprises receiving radio signals at an analog, wideband spectrum-sensing module.

According to yet another embodiment of the present invention, there is a spectrum sensing system. The spectrum sensing system includes a coarse-sensing module that utilizes a wavelet transform to generate a signal indicative of spectrum usage, a spectrum recognition module in communication with the coarse sensing module that determines an occupied spectrum segment based at least partially on the signal from the course sensing module, and a fine-sensing module that generates a signal indicative of a feature of a signal type for an occupied spectrum segment identified by the spectrum recognition module.

According to an aspect of the present invention, the system further includes at least one analog-to-digital converter for digitizing the signal indicative of spectrum usage and the signal indicative of a feature of the signal type, where the digitized signal indicative of spectrum usage and the digitized signal indicative of a feature of the signal type may be provided to the spectrum recognition module. According to another aspect of the present invention, the fine-sensing module may generate a signal indicative of a feature of a signal type based at least in part on a periodic nature of an input signal. The feature of the system type may be associated with at least one of a modulation format and frame structure of the input signal. According to another aspect of the present invention, the spectrum recognition module may be in communication with the fine-sensing module. Likewise, the spectrum recognition module may determine a non-occupied segment based at least partially on the signal from the fine-sensing module. According to yet another embodiment of the present invention, at least one of the coarse-sensing module and the fine-sensing module may operate in an analog domain.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 illustrates a functional block diagram of an exemplary cognitive radio system in accordance with an embodiment of the present invention.

FIG. 2 illustrates an exemplary flowchart of the cognitive radio system of FIG. 1.

FIG. 3 illustrates a tradeoff between a wavelet pulse width and a wavelet pulse frequency in accordance with an embodiment of the present invention.

FIG. 4A illustrates a block diagram for an exemplary Multi-Resolution Spectrum Sensing (MRSS) implementation in accordance with an embodiment of the present invention.

FIG. 4B illustrates an example of scalable resolution control in accordance with an embodiment of the present invention.

FIG. 5A illustrates the waveform of a two-tone signal and FIG. 5B illustrates the corresponding spectrum to be detected with the MRSS implementation in accordance with an embodiment of the present invention.

FIG. 6 illustrates a waveform of the chain of wavelet pulses in accordance with an embodiment of the present invention.

FIG. 7A illustrates the I-component waveform of the I-Q sinusoidal carrier, and FIG. 7B illustrates the Q-component waveform of the I-Q sinusoidal carrier in accordance with an embodiment of the present invention.

FIG. 8A illustrates modulated wavelet pulses obtained from a wavelet generator with an I-component of an I-Q sinusoidal carrier in accordance with an embodiment of the present invention.

FIG. 8B illustrates the modulated wavelet pulses obtained from a wavelet generator with a Q-component of an I-Q sinusoidal carrier in accordance with an embodiment of the present invention.

FIG. 9A illustrates a correlation output signal waveform for the input signal with the I-component of the I-Q sinusoidal carrier in accordance with an embodiment of the present invention.

FIG. 9B illustrates the correlation output signal waveform for the input signal with the Q-component of the I-Q sinusoidal carrier in accordance with an embodiment of the present invention.

FIG. 10A illustrates sampled values via the integrator and the analog-to-digital converter for the correlation values with the I-component of the wavelet waveform within given intervals in accordance with an embodiment of the present invention.

FIG. 10B illustrates sampled values via the integrator and the analog-to-digital converter for the correlation values with the Q-component of the wavelet waveform within given intervals in accordance with an embodiment of the present invention.

FIG. 11 illustrates an exemplary spectrum shape detected by the spectrum recognition module in the MAC module in accordance with an embodiment of the present invention.

FIGS. 12-17 illustrate simulations of various signal formats detected by MRSS implementations in accordance with embodiments of the present invention.

FIG. 18 illustrates an exemplary circuit diagram of the coarse sensing module in accordance with an embodiment of the present invention.

FIG. 19 illustrates a functional block diagram of an exemplary fine-sensing technique utilizing the AAC function in accordance with an embodiment of the present invention.

FIG. 20A illustrates an exemplary data OFDM symbol followed by a preamble in accordance with an embodiment of the present invention.

FIG. 20B illustrates the spectrum of an input IEEE802.11a signal to be detected with an AAC implementation in accordance with an embodiment of the present invention.

FIG. 21A illustrates an input IEEE802.11a signal and FIG. 21B illustrates a delayed IEEE 802.11a signal in accordance with an embodiment of the present invention.

FIG. 22 illustrates a waveform of a correlation between the original input signal and the delayed signal in accordance with an embodiment of the present invention.

FIG. 23 illustrates a waveform produced by an integrator in accordance with an embodiment of the present invention.

FIG. 24 illustrates an exemplary configuration for a frequency-agile radio front-end in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

Embodiments of the present invention relate to cognitive radio systems, methods, and apparatuses for exploiting limited spectrum resources. The cognitive radios may allow for negotiated and/or opportunistic spectrum sharing over a wide frequency range covering a plurality of mobile communication protocols and standards. In accordance with the present invention, embodiments of the cognitive radio may be able to intelligently detect the usage of a segment in the radio spectrum and to utilize any temporarily unused spectrum segment rapidly without interfering with communications between other authorized users. The use of these cognitive radios may allow for a variety of heterogeneous wireless networks (e.g., using different communication protocols, frequencies, etc.) to coexist with each other. These wireless networks may include cellular networks, wireless personal area networks (PAN), wireless local area networks (LAN), and wireless metro area networks (MAN). These wireless networks may also coexist with television networks, including digital TV networks. Other types of networks may be utilized in accordance with the present invention, as known to one of ordinary skill in the art.

A. System Overview of Cognitive Radios

FIG. 1 illustrates a functional block diagram of an exemplary cognitive radio system in accordance with an embodiment of the present invention. In particular, FIG. 1 illustrates a cognitive radio 100 that includes an antenna 116, a transmit/receive switch 114, a radio front end 108, an analog wideband spectrum-sensing module 102, an analog to digital converter 118, a signal processing module 126, and a medium access control (MAC) module 124.

During operation of the cognitive radio system of FIG. 1, which will be discussed in conjunction with the flowchart of FIG. 2, radio frequency (RF) input signals may be received by the antenna 116. In an exemplary embodiment of the present invention, the antenna 116 may be a wideband antenna operable over a wide frequency range, perhaps from several megahertz (MHz) to the multi-gigahertz (GHz) range. The input signals received by the antenna 116 may be passed or otherwise provided to the analog wideband spectrum-sensing module 102 via the transmit/receive switch 114 (block 202). The spectrum-sensing module 102 may include one or both of a coarse-sensing module 104 and a fine-sensing module 106. As their names suggest, the coarse-sensing module 104 may detect the existence or presence of suspicious spectrum segments (e.g., potentially utilized spectrum segments) while the fine-sensing module 106 may scrutinize or otherwise analyze the detected suspicious spectrum segments to determine the particular signal types and/or modulation schemes utilized therein.

Referring back to FIG. 2, the coarse-sensing module 104 may initially determine the spectrum occupancy for the received input signal (block 204). The spectrum occupancy information may be converted from analog form to digital form by the analog-to-digital (A/D) converter 118, which may be a low-speed A/D converter (ADC) in an exemplary embodiment of the present invention. The digital spectrum occupancy information provided by the A/D converter 118 may be received by the spectrum recognition module 120 in the medium access control (MAC) module 124. The spectrum recognition module 120 may perform one or more calculations on the digital spectrum occupancy information to recognize whether one or more spectrum segments are currently in use or occupied by others. The spectrum recognition module 120 may be implemented in hardware, software, or a combination thereof.

In some instances, based on the recognized spectrum segments, the MAC module 124 may request a more refined search of the spectrum occupancy (block 206). In such a case, the fine-sensing module 106 may be operative to identify the particular signal types and/or modulation schemes utilized within at least a portion of the spectrum occupancy (block 208). The information identifying the signal types and/or modulation schemes may then be digitized by the A/D converter 118, and provided to the spectrum recognition module 120. Information about the signal type and/or modulation scheme may be necessary to determine the impact of interferers within the detected suspicious spectrum segments.

In accordance with an embodiment of the present invention, the spectrum recognition module 120 may compare information from the coarse-sensing module 104 and/or fine-sensing module 106 with a spectrum usage database (block 210) to determine an available (e.g., non-occupied or safe) spectrum slot (block 212). The spectrum usage database may include information regarding known signal types, modulation schemes, and associated frequencies. Likewise, the spectrum usage database may include one or more thresholds for determining whether information from the coarse-sensing module 104 and/or fine-sensing module 106 is indicative of one or more occupied spectrum. According to an exemplary embodiment of the present invention, the spectrum usage database may be updated based upon information received from an external source, including periodic broadcasts form a base station or other remote station, removable information stores (e.g., removable chips, memory, etc.), Internet repositories. Alternatively, the spectrum usage database may be updated based upon internally, perhaps based upon adaptive learning techniques that may involve trial and error, test configurations, statistical calculations, etc.

The sensing results determined by the spectrum recognition module 120 may be reported to the controller (e.g., spectrum allocation module) of the MAC module 124, and permission may be requested for a particular spectrum use (block 214). Upon approval from the controller (block 216), the reconfiguration block of the MAC module 124 may provide reconfiguration information to the radio front end 108 via the signal processing module 126 (block 218). In an exemplary embodiment of the present invention, the radio front-end 108 may be reconfigurable to operate at different frequencies (“frequency-agile”), where the particular frequency or frequencies may depend upon the selected spectrum segments for use in communications by the cognitive radio 100. In conjunction with the frequency-agile front-end 108, the signal processing module 126, which may be a physical layer signal processing block in an exemplary embodiment, may enhance the cognitive radio's 100 performance with adaptive modulation and interference mitigation technique.

Many modifications can be made to the cognitive radio 100 without departing from embodiments of the present invention. In an alternative embodiment, the antenna 116 may comprise at least two antennas. A first antenna may be provided for the radio front end 108 while a second antenna may be provided for the spectrum sensing module 102. The use of at least two antennas may remove the necessity of a transmit/receive switch 114 between the radio front end 108 and the spectrum-sensing module 102 according to an exemplary embodiment. However, in another embodiment of the present invention, a transmit/receive switch 114 may still be needed between the transmitter 110 and the receiver 112 of the radio front end 108. In addition, the spectrum sensing module 102, the A/D converter 118, and the MAC module 124 may remain in operation even where the radio front end 108 and signal processing module 126 are not operational or are on standby. This may reduce the power consumption of the cognitive radio 100 while still allowing the cognitive radio 100 to determine the spectrum occupancy.

Having described the cognitive radio 100 generally, the operation of the components of the cognitive radio 100 will now be described in further detail.

B. Spectrum-Sensing Components

Still referring to FIG. 1, the spectrum-sensing module 102 may include the coarse-sensing module 104 and a fine-sensing module 106, according to an exemplary embodiment of the present invention. However, other embodiments of the present invention may utilize only one of the spectrum-sensing module 102 or the coarse-sensing module 104 as necessary. In addition, while the spectrum-sensing module 102 has been illustrated as a component of an exemplary cognitive radio 100, such a spectrum-sensing module 102 may be embodied in a different device and utilized as an efficient method for determining the available spectrum in alternative applications. These alternative applications may include wireless personal area networks (PANs), wireless local area networks (LANs), wireless telephones, cellular phones, digital televisions, mobile televisions, and global positioning systems.

Now referring to the spectrum-sensing module 102 of FIG. 1, spectrum-sensing module 102 may include the coarse the coarse-sensing module 104 and the fine-sensing module 106, which may be utilized together to enhance the accuracy of the spectrum detection performance by the MAC module 124. In addition, according to an embodiment of the present invention, the spectrum-sensing module 102 may be implemented in an analog domain, which may offer several features. For example, such a spectrum-sensing module 102 implemented in the analog domain may provide for fast detection for a wideband frequency range, low power consumption, and low hardware complexity. The coarse-sensing module 104 and the fine-sensing module 106 of the spectrum-sensing module 102 will now be discussed in further detail below.

1. Coarse-Sensing Module

In accordance with an exemplary embodiment of the present invention, the coarse-sensing module 104 may utilize wavelet transforms in providing a multi-resolution sensing feature known as Multi-Resolution Spectrum Sensing (MRSS). The use of MRSS with the coarse-sensing module 104 may allow for a flexible detection resolution without requiring an increase in the hardware burden.

With MRSS, a wavelet transform may be applied to a given time-variant signal to determine the correlation between the given time-variant signal and the function that serves as the basis (e.g., a wavelet pulse) for the wavelet transform. This determined correlation may be known as the wavelet transform coefficient, which may be determined in analog form according to an embodiment of the present invention. The wavelet pulse described above that serves as the basis for the wavelet transform utilized with MRSS may be varied or configured, perhaps via the MAC module 124, according to an embodiment of the present invention. In particular, the wavelet pulses for the wavelet transform may be varied in bandwidth, carrier frequency, and/or period. By varying the wavelet pulse width, carrier frequency, and/or period, the spectral contents provided through the wavelet transform coefficient for the given signal may be represented with a scalable resolution or multi-resolution. For example, by varying the wavelet pulse width and/or carrier frequency after maintaining them within a certain interval, the wavelet transform coefficient may provide an analysis of the spectral contents of the time-variant signals in accordance with an exemplary embodiment of the present invention. Likewise, the shape of the wavelet pulse may be configurable according to an exemplary embodiment of the present invention.

a. Wavelet Pulse Selection

The selection of the appropriate wavelet pulse, and in particular the width and carrier frequency for the wavelet pulse, for use in MRSS will now be described in further detail. FIG. 3 illustrates the tradeoff between the wavelet pulse width (Wt) 302 and the wavelet pulse frequency (Wf) 304 (e.g., also referred herein as the “resolution bandwidth”) that may be considered when selecting an appropriate wavelet pulse. In other words, as the wavelet pulse width 302 increases, the wavelet pulse frequency 304 generally decreases. As shown in FIG. 3, the wavelet pulse width 302 may be inversely proportional to the wavelet pulse frequency 304.

In accordance with an embodiment of the present invention, an uncertainty inequality may be applied to the selection of a wavelet pulse width (Wt) 302 and resolution bandwidth (Wf) 304. Generally, the uncertainty inequality provides bounds for the wavelet pulse width (Wt) 302 and resolution bandwidth (Wf) 304 for particular types of wavelet pulses. An uncertainty inequality may be utilized where the product of the wavelet pulse width (Wt) 302 and the resolution bandwidth (Wf) 304 may be greater than or equal to 0.5 (i.e., Wt*Wf≧0.5). Equality may be reached where the wavelet pulse is a Gaussian wavelet pulse. Thus, for a Gaussian wavelet pulse, the wavelet pulse width (Wt) 302 and the resolution bandwidth (Wf) 304 may be selected for use in the wavelet transform such that their product is equal to 0.5 according to the uncertainty inequality.

While the Gaussian wavelet pulses have been described above for an illustrative embodiment, other shapes of wavelet pulses may be utilized, including from the Hanning, Haar, Daubechies, Symlets, Coifets, Bior Splines, Reverse Bior, Meyer, DMeyer, Mexican hat, Morlet, Complex Gaussian, Shannon, Frequency B-Spline, and Complex Morlet wavelet families.

b. Block Diagram for MRSS Implementation

FIG. 4A illustrates a block diagram for an exemplary Multi-Resolution Spectrum Sensing (MRSS) implementation that includes a coarse-sensing module 104. In particular, the coarse-sensing module may receive a time-variant RF input signal x(t) from the antenna 116. According to an exemplary embodiment of the present invention, this RF input signal x(t) may be amplified by an amplifier 402 before being provided to the coarse sensing module 104. For example, the amplifier 402 may be a driver amplifier, which may be operative to provide for consistent gain across a wide frequency range.

Referring to the coarse-sensing module 104 of FIG. 4A, the coarse-sensing module 104 may be comprised of an analog wavelet waveform generator 404, an analog multiplier 406, an analog integrator 408, and a timing clock 410. The timing clock 410 may provide timing signals utilized by the wavelet generator 404 and the analog integrator 408. Analog correlation values may be provided at the output of the analog integrator 408, which may in turn be provided to an analog-to-digital converter (ADC) 118, which may be low-speed according to an exemplary embodiment of the present invention. The digitized correlation values at the output of the ADC 118 may be provided to the medium access control (MAC) module 124.

Still referring to FIG. 4A, the wavelet generator 404 of the coarse-sensing module 104 may be operative to generate a chain of wavelet pulses v(t) that are modulated to form a chain of modulated wavelet pulses w(t). For example, the chain of wavelet pulses v(t) may be modulated with I- and Q-sinusoidal carriers f_(LO)(t) having a given local oscillator (LO) frequency. With the I- and Q-sinusoidal carriers f_(LO)(t), the I-component signal may be equal in magnitude but 90 degrees out of phase with the Q-component signal. The chain of modulated wavelet pulses w(t) output by the wavelet generator 404 may then be multiplied or otherwise combined with the time-variant input signal x(t) by the analog multiplier 406 to form an analog correlation output signal z(t) that is input into the analog integrator 408. The analog integrator 408 determines and outputs the analog correlation values y(t).

These analog correlation values y(t) at the output of the analog integrator 408 are associated with wavelet pulses v(t) having a given spectral width that is based upon the pulse width and the resolution bandwidth discussed above. Referring back to the coarse-sensing module 104 of FIG. 4A, the wavelet pulse v(t) is modulated using the I- and Q-sinusoidal carriers f_(LO)(t) to form the modulated wavelet pulses w(t). The local oscillator (LO) frequency of the I- and Q-sinusoidal carriers f_(LO)(t) can then be swept or adjusted. By sweeping the I- and Q-sinusoidal carriers f_(LO)(t), the signal power magnitudes and the frequency values within the time-variant input signal x(t) may be detected in the analog correlation values y(t) over a spectrum range, and in particular, over the spectrum range of interest, thereby providing for scalable resolution.

For example, by applying a narrow wavelet pulse v(t) and a large tuning step size of the LO frequency f_(LO)(t), an MRSS implementation in accordance with an embodiment of the present invention may examine a very wide spectrum span in a fast and sparse manner. By contrast, very precise spectrum searching may be realized with a wide wavelet pulse v(t) and the delicate adjusting of the LO frequency f_(LO)(t). Moreover, in accordance with an exemplary embodiment of the present invention, this MRSS implementation may not require any passive filters for image rejection due to the bandpass filtering effect of the window signal (e.g., modulated wavelet pulses w(t)). Likewise, the hardware burdens, including high-power consuming digital hardware burdens, of such an MRSS implementation may be minimized. FIG. 4B illustrates an example of such scalable resolution control in the frequency domain with the use of wavelet pulses W(ω). In particular, FIG. 4B illustrates that an input signal W(ω) can be multiplied 406 with wavelet pulse W(ω) having varying resolution bandwidths to achieve scalable resolution control of the various output correlation values Y(ω).

Referring back to FIG. 4A, once the analog correlation values y(t) have been generated by the analog integrator 408, the magnitudes of the coefficient values y(t) may be digitized by the analog-to-digital converter 118 and provided to the MAC module 124. More specifically, the resulting analog correlation values y(t) associated with each of the I- and Q-components of the wavelet waveforms may be digitized by the analog-to-digital converter 118, and their magnitudes are recorded by the MAC module 124. If the magnitudes are greater than a certain threshold level, then the sensing scheme, perhaps utilizing the spectrum recognition module 120 in the MAC module 124, may determine a meaningful interferer reception (e.g., a particular detected spectrum occupancy) in accordance with an embodiment of the present invention.

c. Simulation of MRSS Implementation

An Multi-Resolution Spectrum Sensing (MRSS) implementation in accordance with an embodiment of the present invention will now be described with respect to several computer simulations. In particular, a computer simulation was performed using a two-tone signal x(t), where each tone was set at the same amplitude but at a different frequency. The sum of the two tone signals with different frequencies and the phases can be expressed as x(t)=A₁ cos(ω₁t+θ₁)+A₂ cos(ω₂t+θ₂). FIG. 5A illustrates the waveform of the two-tone signal x(t), and FIG. 5B illustrates the corresponding spectrum to be detected with the MRSS implementation in accordance with an embodiment of the present invention.

In accordance with the exemplary simulated MRSS implementation, the Manning window function (e.g., Wt*Wf=0.513) for this exemplary simulated MRSS implementation was chosen as the wavelet window function that bounds the selection of wavelet pulse width Wt and the resolution bandwidth Wf for the wavelet pulses v(t). The Manning window function was used in this simulation because of its relative simplicity in terms of the practical implementation. The uncertainty inequality of Wt*Wf=0.513 discussed above may be derived from the calculations of the wavelet pulse width (Wt) 302 and the resolution bandwidth (Wf) 304 for Hanning wavelet pulses as shown below:

$\begin{matrix} {W_{t}^{2} = {\frac{1}{E}{\int_{- \infty}^{\infty}{t^{2}{v^{2}(t)}{\mathbb{d}t}}}}} \\ {= {\frac{1}{E}{\int_{{- \pi}/\omega_{p}}^{\pi/\omega_{p}}{{t^{2}\left\lbrack {1 + {\cos\left( {\omega_{p}t} \right)}} \right\rbrack}^{2}{\mathbb{d}t}}}}} \\ {= \frac{{2\;\pi^{2}} - 15}{6\;\omega_{p}^{2}}} \end{matrix}$ $\begin{matrix} {W_{f}^{2} = {\frac{1}{2\pi\; E}{\int_{- \infty}^{\infty}{\omega^{2}{{V({j\omega})}}^{2}{\mathbb{d}\omega}}}}} \\ {= {\frac{1}{2\pi\; E}{\int_{- \infty}^{\infty}{\omega^{2}{{\frac{\omega_{p}^{2}}{\omega\left( {\omega_{p}^{2} - \omega^{2}} \right)}{\sin\left( \frac{\omega_{\pi}}{\omega_{p}} \right)}}}^{2}{\mathbb{d}\omega}}}}} \\ {= \frac{\omega_{p}^{2}}{3}} \end{matrix}$

FIG. 6 illustrates the waveform of the exemplary chain of wavelet pulses v(t). Accordingly, a chain of modulated wavelet pulses w(t) may be obtained from the wavelet generator 404 by modulating the I- and Q-sinusoidal carriers f_(LO)(t) with a window signal comprised of a chain of wavelet pulses v(t) in an exemplary embodiment of the present invention. In particular, the modulated wavelet pulses w(t) may be obtained by w(t)=v(t)·f_(LO)(t), where v(t)=I+m cos(ω_(p)t+θ_(p)) and

${{f_{LO}(t)} = {\sum\limits_{k = 1}^{K}{\cos\left( {{k\;\omega_{LO}t} + \Phi} \right)}}},{\Phi = {0\mspace{14mu}{or}\mspace{14mu} 90{{^\circ}.}}}$ FIG. 7A illustrates the I-component waveform of the T-Q sinusoidal carrier f_(LO)(t), and FIG. 7B illustrates the Q-component waveform of the I-Q sinusoidal carrier f_(LO)(t). FIG. 8A illustrates the modulated wavelet pulses w(t) obtained from the wavelet generator 404 with the I-component of the I-Q sinusoidal carrier f_(LO)(t). Likewise, FIG. 8B illustrates the modulated wavelet pulses w(t) obtained from the wavelet generator 404 with the Q-component of the I-Q sinusoidal carrier f_(LO)(t).

Each modulated wavelet pulse w(t) is then multiplied by the time-variant signal x(t) by an analog multiplier 406 to produce the resulting analog correlation output signals z(t), as illustrated in FIGS. 9A and 9B. In particular, FIG. 9A illustrates the correlation output signal z(t) waveform for the input signal x(t) with the I-component of the I-Q sinusoidal carrier f_(LO)(t) while FIG. 9B illustrates the correlation output signal z(t) waveform for the input signal x(t) with the Q-component of the I-Q sinusoidal carrier f_(LO)(t). The resulting waveforms in FIGS. 9A and 9B are then integrated by the analog integrator 408 to obtain the correlation values y(t) of the input signal x(t) with the I- and the Q-component of the wavelet waveform w(t).

The correlation values y(t) can then be integrated by the analog integrator 408 and sampled by the analog-to-digital converter 118. FIG. 10A shows the sampled values y_(t) provided by the analog-to-digital converter 118 for these correlation values y(t) with the I-component of the wavelet waveform w(t) within the given intervals. FIG. 10B shows the sampled values y_(Q) via the analog integrator 408 and the analog-to-digital converter 118 for the correlation values with the Q-component of the wavelet waveform w(t) within the given intervals. The MAC module 124, and perhaps its constituent spectrum recognition module 120, then calculates the magnitudes of those sampled values by taking the square-root for those values, y_(I) and y_(Q), as shown in by |y|=√{square root over (y_(I) ²(t)+y_(Q) ² (t))}{square root over (y_(I) ²(t)+y_(Q) ² (t))} according to an exemplary embodiment of the present invention. The spectrum shape detected by the spectrum recognition module 120 in the MAC module 124 is shown in FIG. 11. As shown in FIG. 11, the detected spectrum shape is well-matched with the expected spectrum shown in FIG. 5B, thereby signifying good detection and recognition of the expected spectrum.

FIGS. 12-17 illustrate simulations of various signal formats detected by exemplary MRSS implementations in accordance with embodiments of the present invention. These signal formats may include GSM, EDGE, wireless microphone (FM), ATDC (VSB), 3G cellular—WCDMA, IEEE802.11a—WLAN (OFDM). In particular, FIG. 12A illustrates the spectrum of a GSM signal and FIG. 12B illustrates the corresponding detected signal spectrum. Likewise, FIG. 13A illustrates the spectrum of an EDGE signal and FIG. 13B illustrates the corresponding detected signal spectrum. FIG. 14A illustrates the spectrum of a wireless microphone (FM) signal and FIG. 14B illustrates the corresponding detected signal spectrum. FIG. 15A illustrates the spectrum of an ATDC (VSB) signal and FIG. 15B illustrates the corresponding detected signal spectrum. FIG. 16A illustrates the spectrum of a 3G-cellular (WCDMA) signal and FIG. 16B illustrates the corresponding detected signal spectrum. FIG. 17A illustrates the spectrum of an IEEE 802.11a—WLAN (OFDM) signal and FIG. 17B illustrates the corresponding detected signal spectrum. One of ordinary skill in the art will recognize that other signal formats may be detected in accordance with MRSS implementations in accordance with embodiments of the present invention.

d. Circuit Diagram for Coarse-Sensing Block

An exemplary circuit diagram of the coarse sensing module 104 shown in FIG. 4 is illustrated in FIG. 18. More specifically, FIG. 18 illustrates a wavelet generator 454, multipliers 456 a and 456 b, and integrators 458 a and 458 b. The wavelet generator 454 may be comprised of a wavelet pulse generator 460, a local oscillator (LO) 462, a phase shifter 464 (e.g., a 90° phase shifter), and multipliers 466 a and 466 b. The wavelet pulse generator 460 may provide envelope signals that determines the width and/or shape of the wavelet pulses v(t). Using multiplier 466 a, the wavelet pulse v(t) is multiplied by the I-component of the LO frequency provided by the LO 462 to generate the I-component modulated wavelet pulse w(t). Likewise, using multiplier 466 b, the wavelet pulse v(t) is multiplied by the Q-component of the LO frequency, as shifted 90° by the phase shifter 464, to generate the Q-component modulated wavelet pulse w(t).

The respective I- and Q-components of the modulated wavelet pulse w(t) are then multiplied by the respective multipliers 456 a and 456 b to generate the respective correlation output signals z_(I)(t) and z_(Q)(t). The correlation output signals z_(I)(t) and z_(Q)(t) are then integrated by the respective integrators 458 a and 458 b to yield respective correlation values y_(I)(t) and y_(Q)(t). While FIG. 18 illustrates a specific embodiment, one of ordinary skill in the art will recognize that many variations of the circuit diagram in FIG. 18 are possible.

2. Fine-Sensing Module

In accordance with an exemplary embodiment of the present invention, the fine-sensing module 106 of FIG. 1 may be operative to recognize the periodic features of the input signals unique for each suspect modulation format or frame structure. These periodic features may include sinusoidal carriers, periodic pulse trains, cyclic prefixes, and preambles. More specifically, the fine-sensing module 106 may implement one or more correlation functions for recognizing these periodic features of the input signals. The recognized input signals may include a variety of sophisticated signal formats adopted in the current and emerging wireless standards, including IS-95, WCDMA, EDGE, GSM, Wi-Fi, Wi-MAX, Zigbee, Bluetooth, digital TV (ATSC, DVB), and the like.

According to an embodiment of the present invention, the correlation function implemented for the fine-sensing module 106 may be an Analog Auto-Correlation (AAC) function. The AAC function may derive the amount of the similarity (i.e., the correlation) between two signals. In other words, the correlation between the same waveforms produces the largest value. However, because the data modulated waveform has a random feature because the underlying original data includes random values, the correlation between the periodic signal waveform and the data modulated signal waveform may be ignored. Instead, the periodic feature of a given signal (e.g., modulation format or frame structure) has a high correlation that may be utilized by the AAC function as the signature for the specific signal type. The specific signal type identified by the AAC function in the fine-sensing module 106 may be provided to the signal processing module 126 for mitigation of interference effects.

a. Block Diagram of AAC Implementation

FIG. 19 illustrates a functional block diagram of an exemplary fine-sensing module 106 utilizing the AAC function in accordance with an embodiment of the present invention. In particular, the fine-sensing module 106 may include an analog delay module 502, an analog multiplier 504, an analog integrator 506, and a comparator 508. The analog correlation values provided at an output of the fine-sensing module 106 may be digitized by an analog-to-digital converter 118, which may be low-speed according to an embodiment of the present invention.

Now referring to the fine-sensing module 106 of FIG. 19, an input RF signal x(t) from the antenna 116 is delayed by a certain delay value T_(d) by the analog delay module 502. The delay value T_(d) provided by the analog delay block 502 may be a predetermined and unique value for each periodic signal format. For example, an IEEE 802.11a—WLAN (OFDM) signal may be associated with a first delay value T_(d1) while a 3G-cellular (WCDMA) signal may be associated with a second delay value T_(d2) different from the first delay value T_(d1).

The analog correlation between the original input signal x(t) and the corresponding delayed signal x(t−T_(d)) may be performed by multiplying or otherwise combining these two signals—the original input signal x(t) and the delayed signal x(t−T_(d))—with an analog multiplier 504 to form a correlation signal. The correlation signal is then integrated with an analog integrator 506 to yield correlation values. The analog integrator 506 may be a sliding-window integrator according to an exemplary embodiment of the present invention. When correlation values from the integrator 506 are greater than a certain threshold as determined by the comparator 508, the specific signal type for the original input signal may be identified by the spectrum recognition module 120 of the MAC module 124. According to an embodiment of the present invention, the threshold may be predetermined for each signal type. These signal types can include IS-95, WCDMA, EDGE, GSM, Wi-Fi, Wi-MAX, Zigbee, Bluetooth, digital TV (ATSC, DVB), and the like.

Because the exemplary AAC implementation in FIG. 19 processes all the signals in the analog domain, this may allow not only for real-time operation but also low-power consumption. By applying a delay T_(d) and thus a correlation to the input signal, a blind detection may achieved with no need of any known reference signals. This blind detection may drastically reduce the hardware burden and/or power consumption for the reference signal recovery. Moreover, in accordance with an embodiment of the present invention, the AAC implementation of FIG. 19 may enhance the spectrum-sensing performance when provided in conjunction with the MRSS implementation described above. In particular, once the MRSS implementation detects the reception of a suspicious interferer signal, the AAC implementation may examine the signal and identify its specific signal type based upon its signature.

b. Simulation of the AAC Implementation

In accordance with an embodiment of the present invention, the AAC implementation of FIG. 19 may be simulated for a variety of signal types. As an example, an IEEE 802.11a—OFDM (Orthogonal Frequency Division Multiplexing) signal may always have synchronization preambles at the beginning of a frame structure. For the simplicity, only one exemplary data OFDM symbol 552 may be followed by an exemplary preamble 551 as shown in FIG. 20A. FIG. 20B illustrates the spectrum of the input IEEE 802.11a signal to be detected with an AAC implementation in accordance with an embodiment of the present invention.

FIG. 21A illustrates the input IEEE 802.11a signal x(t) and FIG. 21B illustrates the delayed IEEE 802.11a signal x(t−T_(d)). FIG. 22 illustrates a waveform of a correlation between the original input signal x(r) and the delayed signal x(t−T_(d)), as provided at an output of the multiplier 504. The resulting correlation waveform shown in FIG. 22 may have consecutive positive values 554 for the preambles 551. The result of the integrator 506 as shown in FIG. 23 may have peaks 602, 604 for the preamble 551 locations within the IEEE 802.11a frame structure. Meanwhile, the correlation for the modulated data symbols 552 has random values 556, which can be ignored after integration by the analog integrator 506. By comparing the predetermined threshold Vth utilizing a comparator 508 with the resulting waveform shown in FIG. 23, the exemplary AAC implementation of FIG. 19 may determine the reception of the IEEE 802.11a—OFDM signal.

Many variations of the AAC implementation described with respect to FIG. 19 are possible. In an alternative embodiment, the output of the integrator 506 may be digitized by the analog-to-digital converter 118 before a comparison to the threshold Vth is performed by comparator 508. While the analog-to-digital converter 118 may be shared between the coarse-sensing module 104 and the fine-sensing module 106 in one embodiment, separate analog-to-digital converters may be provided for both the coarse-sensing module 104 and the fine-sensing module 106 in other embodiments. Likewise, the multiplier 504 and the integrator 506 of the fine-sensing module 106 may either be the same as or distinct from the multiplier 406 and the integrator 408 in the coarse-sensing module 104. Many other variations will be known to one of ordinary skill in the art.

C. Signal Processing Block

Referring back to FIG. 1, a signal processing module 126 is disclosed, which may be a physical layer block according to an exemplary embodiment of the present invention. The signal processing module 126 may provide baseband processing, including one or more modulation and demodulation schemes. In addition, the signal processing module 126 may also provide interference mitigation, perhaps based upon any identified interferer signals. Furthermore, the signal processing module 126 may be operative to reconfigure the radio front-end, including the transmitter 110 and/or receiver 112, perhaps based at least in part upon the available spectrum. For example, the signal processing block may adjust the transmission power control for the transmitter 110 or tune a filter for the receiver 112 to operate within a particular frequency range. One of ordinary skill in the art will readily recognize that other baseband processing may be provided by the signal processing module 126 as necessary or desirable.

D. Frequency-Agile Radio Front End

FIG. 24 illustrates an exemplary configuration for a frequency-agile radio front-end 108 in accordance with an embodiment of the present invention. In particular, the receive portion of the radio front-end 108 may include one or more tunable filters 702, a wideband receiver 704, and one or more low pass filters 706. The tunable filter 702 may comprise a wavelet generator and a multiplier according to an exemplary embodiment of the present invention. The wideband receiver 704 may include one or more frequency stages and one or more downconverters as necessary. In addition, the transmit portion of the radio front-end 108 may include one or more low-pass filters 708, a wideband transmitter 710, and one or more power amplifiers 712. The wideband transmitter 710 may also include one or more frequency stages and one or more upconverters as necessary. Furthermore, the wideband receiver 704 and transmitter 710 may be in communication with a tunable signal generator 714. One of ordinary skill in the art will recognize that the components of the frequency-agile front-end 108 may be varied without departing from embodiments of the present invention.

As stated previously with respect to FIGS. 1 and 2, the MAC module 124 processes the digitized data (e.g., via ADC 118) from the spectrum sensing module 102 to allocate the available spectrum for a safe (e.g., unoccupied or non-interfering) cognitive radio 100 link. Additionally, the MAC module 124 provides the reconfiguration control signal to the radio front-end 108 for the optimal radio link in the allocated frequencies. Then, the radio front-end 108 changes the operating RF frequency to the corresponding frequency value in accordance with its frequency agile operation. More specifically, either or both of the tunable filter 702 and the tunable signal generator 714 may change their operating frequencies to select the signals within the corresponding frequency region. In the meantime, based upon the MAC module 124 control information, the PHY signal processing module 126 may enhance the link performance with the adaptive modulation and interference mitigation technique.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. A cognitive radio system, comprising: at least one antenna; a spectrum-sensing module configured to receive a radio frequency (RF) input signal from the at least one antenna and configured to generate analog radio frequency (RF) spectrum usage information, wherein the spectrum-sensing module processes the received RF input signal in an analog domain to generate the analog RF spectrum usage information; an analog-to-digital converter for digitizing the analog RF spectrum usage information; and a medium access control (MAC) module operative to receive the digitized RF spectrum usage information from the spectrum-sensing module, wherein the MAC module is operative to direct a frequency of operation of a radio front-end module based at least in part on the received spectrum usage information, wherein the spectrum-sensing module operates in parallel with the radio front-end module such that the spectrum-sensing module and radio front-end module are operative independently of each other.
 2. The cognitive radio system of claim 1, wherein the at least one antenna comprises a first antenna and a second antenna, wherein the radio front-end module is in communication with the first antenna and the spectrum-sensing module is in communication with the second antenna.
 3. The cognitive radio system of claim 1, wherein the spectrum-sensing module comprises at least one of a coarse-sensing module and a fine-sensing module, wherein the coarse-sensing module provides spectrum usage information associated with spectrum occupancy and the fine-sensing module provides spectrum usage information associated with signal identification.
 4. The cognitive radio system of claim 3, wherein the spectrum usage information associated with signal identification relates to at least one of modulation schemes and frame types.
 5. The cognitive radio system of claim 1, wherein the spectrum-sensing module generates spectrum usage information associated with spectrum occupancy and upon a request by the MAC module, generates spectrum usage information associated with signal identification.
 6. A method for implementing a cognitive radio system, comprising: receiving radio signals at a spectrum-sensing module; generating via the spectrum-sensing module, analog spectrum information based on processing the received radio signals in an analog domain; digitizing the analog spectrum information; receiving the digitized spectrum information at a medium access control module; determining via the medium access control module, a non-occupied spectrum based at least in part upon the spectrum information; and reconfiguring a transceiver to operate in the non-occupied spectrum, wherein the spectrum-sensing module operates in parallel with the radio front-end module such that the spectrum-sensing module and radio front-end module are operative independently of each other.
 7. The method of claim 6, wherein generating spectrum information comprises generating information for determining spectrum occupancy.
 8. The method of claim 7, wherein generating spectrum information comprises generating information for signal identification upon a request from the medium access control module.
 9. The method of claim 8, wherein the spectrum sensing module comprises a module that generates the information for determining spectrum occupancy.
 10. The method of claim 8, wherein the spectrum sensing module comprises a module that generates the information for signal identification.
 11. A spectrum sensing system, comprising: a coarse-sensing module that applies a wavelet transform to a radio frequency (RF) input signal to generate a signal indicative of spectrum usage, wherein the wavelet transform comprises a plurality of wavelet pulses having a respective wavelet pulse width and carrier frequency, wherein the coarse-sensing module varies at least one of the wavelet pulse width or carrier frequency over a period of time to generate the signal indicative of spectrum usage; a spectrum recognition module in communication with the coarse-sensing module that determines an occupied spectrum segment based at least partially on the signal from the coarse-sensing module; and a fine-sensing module that generates a signal indicative of a feature of a signal type for an occupied spectrum segment identified by the spectrum recognition module.
 12. The system of claim 11, further comprising at least one analog-to-digital converter for digitizing the signal indicative of spectrum usage and the signal indicative of a feature of the signal type, wherein the digitized signal indicative of spectrum usage and the digitized signal indicative of a feature of the signal type are provided to the spectrum recognition module.
 13. The system of claim 11, wherein the fine-sensing module generates a signal indicative of a feature of a signal type based at least in part on a periodic nature of an input signal.
 14. The system of claim 13, wherein the feature of the system type is associated with at least one of a modulation format and frame structure of the input signal.
 15. The system of claim 11, wherein the spectrum recognition module is in communication with the fine-sensing module.
 16. The system of claim 11, wherein the spectrum recognition module determines a non-occupied segment based at least partially on the signal from the fine-sensing module.
 17. The system of claim 11, wherein at least one of the coarse-sensing module and the fine-sensing module perform processing in an analog domain. 